MTN not honour contract

I upgraded to Sim-only MTN Mega Gigs Black Friday contract for 500 All-net Minutes and 10 GB Anytime Data. MTN gave me only 200 minutes All-net Minutes. They do not honour their contract with me. I went to the MTN shop, phone their 135 number, report it as ***** and launched about 12 tickets of complain, but the matter is still unresolved. The MTN shop contacted the area an regional manager and nobody wants to speak we me over the phone! I have a contract with MTN and they do not honour it from their side, expected from me to pay up.